This invention relates to a flexible coupling for freely rockably coupling a rotary shaft of an electric motor of an electric locomotive and a driven shaft of a gear unit incorporated into wheels on the bogie.
The bogie of an electric locomotive comprises a spring between the wheels and the bogie frame for a comfortable ride. The electric motor is mounted to the bogie frame and the gear unit for driving the axle is incorporated into the wheel shaft. Therefore, a flexible coupling is provided between the sprung electric motor and the unsprung gear unit in order that the shakes, vibrations and noise may not be directly transmitted to the motor side.
An example of the structure of the conventional flexible coupling is disclosed in Japanese Utility Model Publication No. 47-14804. FIG. 7 is a sectional view of this flexible coupling. In the FIG. 7, 1 and 11 are rotary shafts, 2 and 12 are pinions secured to the rotary shafts 1 and 11 and each has formed thereon a crowned outer teeth gear 2a or 12a. Sleeves 3 and 13 are fastened together by bolts and have formed inside inner teeth gears 3a and 13a which are in mesh with the outer teeth gears 2a and 12a of the pinions 2 and 12. End cover 4 and 14 are secured to the sleeves, respectively at one end and extend at the other ends into an annular groove formed in the securing portion of the pinions 2 and 12.
A partition plate 5 is inserted between the joining surfaces of the sleeves 3 and 13 for partitioning the sleeves 3 and 13 from each other. Shaft end nuts 6, 16 are for securing the pinions 2 and 12 onto the rotary shafts 1 and 11, and 7 cushions 7 and 17 are secured to the end shaft nuts 6 and 16 for positioning the shaft end nuts 6 and 16 relative to the partition plate 5 for establishing a proper engagement between the inner teeth gears of the sleeves 3 and 13 and the outer teeth gears of the pinions 2 and 12. The flexible coupling of the above structure is connected to a motor rotary shaft at either the rotary shaft 1 or 11 and to the gear unit combined with the wheel shaft of the bogie.
In the conventional flexible coupling of the above construction, when the axes of the rotary shaft of the electric motor and the gear unit incorporated into the axle come out of alignment, such as when the bogie shakes during the travel of the electric locomotive, the axes of the pinions 2 and 12 at the opposite ends of the coupling displace as shown in FIG. 8. Even when such displacement occurs the crowned outer teeth gears 2a and 12a of the pinions 2 and 12 always engage the inner teeth gears 3a and 13a of the sleeves 3 and 13, to thereby to achieve smooth transmission of the driving power.
In recent years, the speed of the electric locomotive has been significantly increased by increasing the rotational speed of the electric motor and by decreasing the size of the motor to make the overall vehicle weight small. While the increase of the motor speed significantly contributes to the decrease in weight, it also causes vibrations and noise to increase, whereby the comfort of the locomotive ride is degraded. When the motor speed increases and the flexible coupling is being driven at a high speed, precession vibration or torsional vibration may occur because the sleeves are rockable due of the backlash between the meshing portions of the gears of the pinions 2 and the sleeves 3 and because of the possible unbalance as a rotating body.
The conventional crowning of the gears of the flexible coupling is as shown in FIG. 9. FIG. 10 is a side view of the outer teeth gear of the pinion 2. In FIG. 9, 3a is an inner teeth gear of the sleeve 3 and 2a is an outer teeth gear of the pinion 2. As shown in FIG. 10(a), the outer teeth gears 2a of the pinion 2 are rounded by machining so that they smoothly mesh with the inner teeth gears on the sleeves even when the pair of the rotary shafts come out of alignment relative to each other. Also, they are crowned in the tooth thickness direction as shown in FIG. 9 showing the cross section along the pitch circle cylinder.
In these figures, S is the pitch circle diameter, T is the tooth thickness at the pitch circle diameter S of the outer tooth gear 2a of the pinion 2, H is the inner tooth clearance at the pitch circle diameter S of the inner tooth gear 3a of the sleeve 3, G is the backlash, R.sub.c is the radius of the crowning of the outer tooth gear 2a, .beta..sub.w is the allowable displacement angle between the center lines of the sleeve 3 and the pinions 2, and .beta. is the displacement angle. The backlash G at the pitch circle diameter S is expressed by the equation 8 given below and the dimensional relationship between the outer tooth gear 2a and the inner tooth gear 3a at the pitch circle diameter S is expressed by the equation 9 given below. EQU G=(2.multidot.R.sub.c -T).multidot.(1-cos .beta..sub.w) (Equation 8) EQU R.sub.c =(1/2).multidot.{[G/(1-cos .beta..sub.w)]+T)} (Equation 9)
where, R.sub.c : radius of crowning curve
G: backlash PA1 .beta..sub.w : allowable displacement angle PA1 T: tooth thickness PA1 X: axial distance from the origin (O) at the tooth surface at the center of the tooth thickness, and PA1 m: factor n: exponential number PA1 X: axial distance from the origin (O) at the tooth surface at the center of the tooth thickness, and PA1 m: factor n: exponential number PA1 X: axial distance from the origin (O) at the tooth surface at the center of the tooth thickness, and PA1 m: factor n: exponential number PA1 X: axial distance from the origin (O) at the tooth surface at the center of the tooth thickness, and PA1 m: factor PA1 n: exponential number PA1 .beta.w: the allowable displacement angle PA1 G: backlash PA1 xw: the point at which the tooth is brought into contact with the inner tooth gear of the sleeve at the allowable displaced angle .beta.w from the center of the tooth width.
In the flexible coupling of this construction, in order to give a necessary allowable displacement angle .beta..sub.w, the angle of the tangent line at the tooth width end of the crowned surface at the pitch circle S of the outer tooth gear of the pinion 2 relative to the axis of the pinion 2 should be equal to the allowable displacement angle .beta..sub.w, and the gap between the outer tooth gear and the inner tooth gear at the pitch circle diameter S when the displacement angle .beta. should be equal to the backlash G, and it was necessary that G=0.8-1.2 mm in order that the allowable displacement angle .beta..sub.w be 0.1 (.beta..sub.w =about 6 degrees), for example. FIG. 11 shows the state of engagement when the allowable displacement angle is .beta..sub.w.
Thus, the engagement in the direction perpendicular to the direction of displacement is in the state in which the backlash G generates, and the center of rotation of the sleeve 3 displaces within the range of the backlash G, thereby generating an unbalance as a rotating body which may cause the precession vibration and the torsional vibration due to the play in the direction of rotation.
Also, in the typical crowned gear flexible coupling, the number of teeth of the sleeve 3 or pinion 2 which are in simultaneous contact with each other decreases as the displacement angle .beta. increases when the flexible coupling transmitting a constant force rotates. One example of this phenomenon is illustrated in FIG. 12. In the conventional flexible coupling, the gear teeth are crowned at a constant radius of curvature R.sub.c, so that, as the number of the simultaneously contacting teeth decreases, the contacting stress at the tooth surface inverse proportionally increases, increasing the possibility of roughening and damaging the tooth surface.
As described above, the tooth surface is crowned at a constant radius of curvature in the conventional flexible coupling and the backlash defined between the meshing portions of the outer tooth gear of the pinion and the inner tooth gear of the sleeve is made large in order to establish a necessary allowable displacement angle, so that precession vibration and torsional vibration appear as the rotational speed increases to degrade the comfort of ride of the electric locomotive, making it impossible to increase the rotational speed.
Also, since the conventional flexible coupling in which the gear is crowned at a constant radius of curvature has a large backlash, the number of the simultaneously meshing teeth decreases as the displacement increases, so that the stress at the contacting portions of the tooth surface increases substantially in inverse proportion to the displacement angle, posing the problem that roughening and damaging of the tooth surface easily occur.